Unable to use Opera after Windows upgrade

After the latest large Windows update, I became unable to access many sites with Opera, including Google and even opera.com (I am using Edge to write this). The same happened with Chrome and, to a lesser extent, with Firefox. The only browser that works normally is, not surprisingly, Edge.

I looked everywhere and tried several procedures to solve this, without any success. Finally, I decided to revert to an older Windows backup (from January 2018). This did the trick and Opera was again working normally. However, when Windows got itself automatically updated, Opera again stopped accessing the same sites.